The invention relates to the collection of samples of body liquid for allowing analysis thereof, i.e. determination of an analyte concentration therein. In particular it relates to instruments and systems for producing a small sample of body liquid by piercing the skin of a subject (human or animal) using a disposable lancing element having a skin piercing tip suitable for generating a small wound from which the sample is drawn. Depending on the skin site used and on the lancing depth the body liquid is blood or interstitial liquid or a mixture thereof.
Analysis based on skin-piercing is important in several fields of medical diagnostics and treatment. Of particular importance is the field of diabetes management. It has been determined that severe long term damages caused by diabetes mellitus can be avoided if the patient controls her or his blood sugar level several times a day in order to adapt the required insulin injections closely to the actual need for maintaining a constant blood sugar level. This requires so called “home-monitoring” by the patient himself or by other people not having a medical training.
Other important fields of medical diagnostics and treatment with similar requirements, including home-monitoring, refer for example to the regular control of blood cholesterol and to the control of blood coagulation parameters. The invention is in particular suitable but not limited to home-monitoring applications. Similar requirements also exist, e.g., in so called “near-patient-testing”.
Lancing of the skin is generally performed by a lancing system comprising, as mutually adapted components of the system, a reusable hand-held instrument and lancing elements. The movement required for lancing (puncturing movement) is driven by a lancing drive provided inside a housing of the instrument and adapted for driving a lancing element connected thereto. Lancets can be interchangeably connected to the drive and generally are disposable items.
After triggering the puncturing movement the lancet is driven in a puncture direction until it reaches a point of maximum displacement and thereafter it is further driven in a reverse direction. Many suitable lancet drive mechanisms have been described. In most cases the driving force is supplied by a tensioned spring and the lancet drive further includes suitable mechanical means for converting the force of the spring into the required movement of a lancet.
An important consideration in developing lancing systems is the pain caused by the pricking action. This pain and the convenience of use are decisive factors determining compliance of the patient, i.e. his willingness to perform regular analyses as required for maintaining his health. It has been determined that reliable production of the required amount of sample liquid with minimum pain highly depends on the reproducibility of an optimum penetration depth of the tip of the lancing element into the skin (see U.S. Pat. No. 5,318,584).
With earlier lancet systems the analysis generally required a plurality of steps to be performed by the user. After lancing with such earlier systems the blood did not readily emanate from the wound site in the lanced skin. Therefore manual “milking” steps such as pinching, squeezing and kneading where necessary in order to express the required amount of sample liquid. Finally sample liquid was contacted to an analysis element of an analysis system (which was separate and distinct from the lancing system) and the analysis was performed thereby.
In order to improve the production of sample liquid at the lancing site and to avoid the manual “milking” several proposals were made all of which relate to the design of the contact area at a distal end of the lancing instrument having a (generally ring-shaped) skin contact surface surrounding a skin contact opening. Such lancing systems are described in WO 99/26539, WO 01/89383 A2, EP 1 245 187 A1, EP 1 586 269, EP 1 586 270.
While these approaches differ in several ways, a common feature thereof is that the skin contact opening has a relatively large diameter whereby the skin bulges into the skin contact opening forming a target site bulge which penetrates to some extent into the opening when the lancing instrument is pressed with its distal end (i.e. with the skin contact surface) against the skin. This bulging action (hereafter designated “target site bulging”) is generally combined with additional means for improving sample liquid production, such as a mechanical squeezing acting radially inwardly, a pumping action involving axial movement of parts of the instrument, etc.
Ideally these measures allow with a high success rate (preferably better than 90%) expression of a sufficient amount of sample liquid without manual “milking”. This again is a requirement of integrated lancing and analysis systems which, in a single instrument, comprise both, means for the lancing-type sample production and means for the analysis. Such integrated systems have been proposed in a plurality of variants which can be assigned to two types, namely    A) “Two unit systems” having—in a single instrument housing—two separate units for lancing and for analysis. Typically the units are moved one after the other to a common skin contact opening (see e.g. EP 1 669 028 A1 and EP 1 736 100 A1)    B) “Single unit systems” operating with a single combined lancing- and analysis unit suitable for performing both functions (lancing and analysis). Most such systems operate with integrated lancing and analysis elements. The two components of such combined lancing and analysis elements are generally manufactured separately but assembled by the manufacturer or at least before use, i.e. before the lancing movement is triggered. In the instrument such elements are processed as a unified item. In other single unit systems both functions (lancing and analysis) are performed by the same unit but a lancing element and an analysis element are provided and processed separately during at least a part of the analytical procedure. Examples of single unit systems are described in the following publications: WO 01/72220, WO 03/009759 A1, EP 1 342 448 A1, EP 1 360 933 A1, EP 1 362 551 A1.
Even though several of the discussed systems, in particular integrated lancing and analysis systems, provide improved results as compared to earlier known devices, there are still substantial shortcomings. There is a need for improvements with respect to several partially contradictory requirements including ease of use, minimum pain and minimum requirements concerning volume, weight and production cost.